1. Field of the Invention
The present invention relates to a fully-enclosed fan-cooled motor for driving a rail vehicle (sometimes also called fully-enclosed motor with outer fans).
2. Description of the Related Art
In a typical rail vehicle (hereinbelow referred to as a “vehicle”), a main motor (or a traction motor) (hereinbelow called the “motor”) is mounted on a chassis arranged below the vehicle body, and the turning effort of this motor is transmitted to the vehicle wheels through a coupling and gearwheel device to move the vehicle. The construction of a conventional motor of this type is for example as shown in FIG. 1.
In this Figure, the arrows indicate the direction of flow of cooling air.
In the conventional motor shown in FIG. 1, there is provided a cylindrical frame 101 constituting a fixed member; a bearing bracket 102 is mounted at one end of this frame 101; a housing 103 is mounted in the central section of the other end of the frame 101; both ends of a rotor shaft 106 are freely rotatably supported by bearings 104, 105 provided respectively in the center of this bearing bracket 102 and housing 103.
A rotor core 107 is fixed in the central section in the axial direction of the rotor shaft 106; rotor bars 108 are embedded in a large number of grooves formed at the periphery of this rotor core 107; the two ends of the respective rotor bars 108 project from the rotor core 107, and these projecting sections are integrally connected by ring-shaped end rings 109, 109 to form a cage rotor of the induction motor. The rotor core 107 is provided with a plurality of ventilation passages 107a passing therethrough in the axial direction and is fixed by means of core holders 110, 110 having similar passages 110a. 
A cylindrical stator core 111 is mounted on the inner periphery of the frame 101; stator coils 112 are accommodated in a large number of grooves formed at the inner periphery of this stator core 111. The coil ends of these stator coils 112 are of a form projecting on both sides of the stator core 111.
A uniform gap 113 is formed between the inner peripheral surface of this stator core 111 and the outer peripheral surface of the rotor core 107. The drive shaft 106a of the rotor shaft 106 projects outside the motor and a coupling for coupling with a drive gearwheel device is mounted on this projecting section of the drive shaft 106a. Also, a ventilation fan 114 is mounted on a section of the rotor shaft 106 within the motor. This ventilation fan 114 has a plurality of vanes 114a arranged radially from its center.
A plurality of exhaust ports 101a are provided along the peripheral direction in a section of this frame 101 facing the front end of this ventilation fan 114. An air intake port (sometimes also called air inlet port) 101b is provided above the side opposite to the drive side of the frame 101 and a ventilation filter 115 is mounted so as to cover this air intake port 101b; a filter 115a for capturing dust is mounted at the external air inlet of this ventilation filter 115.
The entire motor shown in FIG. 1 has a mounting arm (not shown) provided on the frame 101 that is fixed by means of bolts to the chassis frame; the rotary force of the motor is transmitted from the drive device to the vehicle wheels through a coupling connected with the drive shaft 106a of the rotor shaft 106, thereby driving the vehicle.
When this motor is operated, heat is generated by the stator coils 112 and the rotor bars 108, so cooling is performed by passing external air through the interior of the motor. Rise in temperature of the motor is suppressed by this cooling. This cooling action is as follows.
During operation, the ventilation fan 114 is rotated together with the rotor shaft 106, causing the air within the motor to be discharged to outside the motor from the exhaust ports 101a; accompanying this, external air is sucked into the motor from the intake (sometimes also called inlet) 101b. The external air that is sucked into the motor flows into the motor from the inlet 101b through the ventilation filter 115 and then flows to the ventilation fan 114 through the ventilation passages 107a of the rotor core 107, and the gap 113 between the outer periphery of the rotor core 107 and the inner periphery of the stator core 111, and is then discharged to outside the motor from the exhaust ports 101a by rotation of the ventilation fan 114.
In this way, the rotor bars 108 and stator coils 112 are cooled by passage of external air through the motor. It is thereby possible to ensure that the rise in temperature of the rotor bars 108, stator coils 112, bearings 104, 105 and the grease that is used to lubricate these does not exceed the permitted temperature.
However, the external air that is drawn in represents a severely polluted environment in that large quantities of dust are present entrained in the external air around a motor that is mounted on the underfloor chassis of an electric car or the like during vehicle running. Consequently, in a motor according to the conventional example illustrated in FIG. 1, there was the technical problem that, although an attempt was made to clean the external air that was drawn into the motor by capturing the dust by the filter 115a of the ventilation filter 115, with continuous operation, gradual blockage of the filter 115a took place, decreasing the amount of ventilation within the motor; periodic cleaning/maintenance of the filter was therefore required at short intervals, requiring the expenditure of a very considerable amount of labor.
In order to solve this problem, in recent years, efforts are being made to further develop fully-enclosed fan-cooled motors. An example of the construction of such a fully-enclosed fan-cooled motor is shown in FIG. 2 and the description will be given referring to this example. The arrows indicate the direction of flow of the cooling air, just as in the case of the previous Figure.
A bracket 202 is provided at the drive side end of the frame 201, which is of the form of a cylinder provided with a bottom, and a housing 203 is provided in the middle on the opposite side to the drive side. A stator core 204 is provided at the inner periphery of the frame 201.
A rotor shaft 207 is freely rotatably supported by means of bearings 205, 206 respectively mounted on the bracket 202 and housing 203; a rotor core 208 is provided in the middle in the axial direction of this rotor shaft 207. The drive side end 207a of the rotor shaft 207 projects outside the motor and a coupling with a ventilation fan 209 is mounted on this projecting section. A large number of cooling passages 201a of a shape extending in the axial direction are provided at the outer circumferential face of the frame 201. A ventilation passage 202a is provided in the bracket 202, the drive side thereof opening towards the tip of the ventilation fan 209. Also, the side opposite to the drive side is open to the external atmosphere. An air inlet 209a of the ventilation fan 209 on the drive side of the motor forms an external air inlet.
This fully-enclosed fan-cooled motor is provided with a minute gap 210 formed in hook shape so as not to permit penetration of external air to the region of the bearings and is thus of a fully-enclosed form in which the interior of the motor is cut off from the outside.
Thus, during operation, by passing external air, by rotation of the ventilation fan 209, in the axial direction along the ventilation passage 201a at the outer periphery of the frame 201 via the ventilation passage 202a of the bracket 202, the heat from the rotor bars 211 or stator coils 212 transmitted through the stator core 204 and frame 201 from the wall face in the ventilation passages 201a is discharged to the external atmosphere.
In this fully-enclosed fan-cooled motor, since external air is not made to flow through the interior of the motor, there is the advantage that there is no possibility of contamination of the interior of the motor by dust mixed with this external air and, furthermore that, since it is the portion outside the motor that is cooled by the external air, a filter to remove the dust from this external air is unnecessary.
However, in such a typical fully-enclosed fan-cooled motor, although the heat generated by the stator coils 212 can be discharged to the external atmosphere from the ventilation passages 201a by being transmitted through the core 208 and frame 201, there were the following problems, which presented a considerable obstacle to implementing an ideal fully-enclosed fan-cooled motor.
Firstly, the heat generated by the rotor bars 211 was shut in within the motor, and represented a source of so-called local heat generated solely by the rotor.
Secondly, the heat generated by the stator coils 212 and the heat generated by the rotor bars 211 raised the temperature of the bearings 205, 206, constituting a cause of temperature increase of the grease used to lubricate the bearings 205, 206, which is the item, of the various items in the motor, which has the lowest permitted temperature. If the bearing grease is raised to a high temperature, its lubrication life becomes short and, as a result, the maintenance recursiveness (maintenance recurrence or maintenance period) of the motor cannot be extended.
Thus, as a countermeasure, there was no alternative to designing a conventional fully-enclosed fan-cooled motor in such a way as to suppress generation of heat by the rotor, to ensure that the permitted temperature of the bearing grease was secured: the result was to present obstacles to design of a motor having a larger rotor than normal and offering high output with small size and light weight.